Hibernation

Brrr! Winter's here. The freeze is on. And food is hard to find. What's an animal to do? Some creatures find a hideaway and take a long winter rest called hibernation.

BEARZZZZ . . . In winter, black bears (above) and grizzly bears curl up in dens and go to sleep. While hibernating, the bears get energy by "burning" (using up) the fat they stored in their bodies during summer and fall. This fat has to last until spring. To save energy, the bears breathe less often, their hearts beat slowly, and their body temperatures drop a few degrees below normal. Still, they can wake up in a hurry if they have to.

DEEPER SLEEPERS Some kinds of mammals, such as chipmunks, ground squirrels, and woodchucks, are deep hibernators

During hibernation, their hearts may beat only a few times per minute. And their bodies cool down until they're close to freezing. This is called going into torpor. Most deep hibernators hibernate for five to seven months. But they stay in torpor for only days or weeks at a time. Then they warm up to normal body temperatures for a few hours or days. Why? Scientists think they may need some normal sleep too, and warming up lets that happen.

THE SLEEPING ONE Only one kind of bird--the poorwill (above)--hibernates. This bird tucks itself into a hollow log or other sheltered place. Then it sinks so deeply into torpor that you can't see it breathing or feel its heart beat. The poorwill may hibernate for up to three months. No wonder the Hopi Indians call it "the sleeping one."

BATS ON THE WALL When winter comes, many kinds of bats (below) fly to where the weather is warm. But others hibernate.

Hibernating bats clump together in hollow trees and on the damp walls of caves, mines, and cellars. Then they sink into torpor. By snuggling up in groups, the bats use one another's bodies to keep from getting too cold.

COOL QUEENS Many adult insects die in the fall--only their eggs or young survive. But some adults, such as bald-faced hornet queens (below), do not die--they hibernate.

After mating in late summer, these large females crawl into or under big rotting logs. The logs, and the snow on top of them, act as blankets. Even if the insects freeze, special chemicals in their bodies keep them safe.

TOUGH TURTLES

Many turtles and frogs survive winter by burrowing into mud at the bottoms of ponds or lakes. But baby painted turtles (below) don't even try to escape the cold. They hatch in underground nests in the fall. Soon afterward, they pull their heads and legs into their shells as far as they can. Then their bodies cool down along with the soil around them. The turtles' body temperature can even drop below freezing--with no harm done!

WINTER HANG-OUTS Like hornet queens, some adult butterflies also hibernate. They crawl into old buildings, hollow trees, and other sheltered places. There they hang out until winter passes. One of these hibernators is the mourning cloak. It's often the first butterfly to flutter by in spring. And sometimes a warm, sunny day will fool it into flight in the middle of winter!